NetRAID On-line Capacity Expansion under Microsoft Windows-NT

This application note describes how users can take advantage of the NetRAID

On-line Capacity Expansion feature under the

Microsoft NT operating system. The benefit for the user is that new storage

capacity can be added to the NetRAID controller

and can be put on-line for use without rebooting the server. Follow the

steps outlined below to prepare a system for

capacity expansion and then expand a volume. This will provide the user with

an easy process to add storage whenever

needed.

Setting Up Your Array for Capacity Expansion

When using capacity expansion, you should use a single logical drive since

capacity expansion is controlled on a per

logical drive basis. Reconstruction (e.g., adding a drive to an existing

array) can only be done on an array having a

single logical drive. It is also important to plan future storage expansion

into your installation. This will ensure that

you can easily expand capacity without backup/restore operations or

reconfiguration.

It does not matter if NT is already installed or not at this point assuming

NT will reside on a separate drive. If NT must

be installed on the disk array, see the information under "Operating System

and Data on Disk Array". For this example

assume that NT is installed on a drive connected to the embedded SCSI

channel A. The following steps are necessary to

prepare your array for capacity expansion.

1. Connect Drives to the NetRAID Controller.

Connect physical drives to the NetRAID controller. Example: Assume there are

four drives of 4 GB each connected to the

controller.

2. Configure the Disk Array.

Configure your DAC and create a logical drive (this can be done in either

NetRAID Assistant or in Express Tools). If you

create multiple arrays (groups of physical drives), you should know which

logical drive(s) will be designated for capacity

expansion. You should only assign one logical drive per array, otherwise the

logical drive will not be reconstructable.

Save your configuration. For this example, assume the 4x4 GB drives are

configured as a single RAID 5 logical drive. This

will produce a logical drive with 12 GB of real storage capacity.

Note: It is important to initialize your logical drives; if the drives have

been previously configured under an OS, there

can sometimes be residual partition/format information which can

subsequently cause misrepresentation of logical drives

under the NT Disk Administrator.

3. Enable Virtual Sizing.

If not already, enter Express Tools. Select the logical drive to be setup

for capacity expansion by selecting

Objects/Logical Drives/Properties/Virtual Sizing and enabling Virtual

Sizing. Virtual Sizing is enabled on a per logical

drive basis.

Note: Clearing a previous configuration does not reset the Virtual Sizing

setting previously used for a logical drive; use

the Reset to Factory Defaults in Express Tools to disable Virtual Sizing for

all logical drives or manually change the

setting.

4. Start NT and Enter Disk Administrator.

Start NT and enter the Disk Administrator. Here you will see the new logical

drive shown as a single

unpartitioned/unformatted drive of 81,917 MB. Although there is only 12 GB

of real storage space on the logical drive, the

Capacity Expansion feature creates a virtual drive of 81,917 MB.

5. Partition and Format the Drive.

To use the new drive, you must first partition the drive. Create a partition

equal or less than the real storage capacity

(for this example, 12 GB where 1 GB is 1024 cubed). Commit the change and

format the partition. Note: If the partition is

larger than the real storage capacity, the format operation will generate a

message "Warning: NT was unable to complete the

format".

The formatted drive is now ready for use. Assume for this example the drive

is now E: and was partitioned as a primary

partition. Leave the left over virtual storage space (81,917 MB minus 12 GB)

unpartitioned. You can write data up to 12 GB

on the drive. NT will not allow you to write beyond 12 GB and loose any

data.

Reconstruction and New Volumes

After using the array created above, assume you are nearing the 12 GB limit

and you want to add another 4 GB drive to the

existing array. This can be done without downing the server or rebooting the

system.

6. Add Capacity by Reconstruction.

Add the new physical drive to the NetRAID controller by plugging it into an

empty hot swap storage slot. Bring up NetRAID

Assistant under NT. Select the logical drive and the new physical drive.

Then select Logical Drive/Change Config/Add

Capacity. This will reconstruct the current 4 drive RAID 5 array to a 5

drive RAID 5 array. When reconstruction is

complete, the real storage capacity will now be 16 GB. Reconstruction occurs

in the background, so the original 12 GB

volume will still be available during the reconstruction process.

The reconstruction rate is about 80 to 180 MB per minute (depending drive

performance, system loading, etc.). Count the

capacity to be reconstructed as the number of physical drives participating

in the reconstruction times drive capacity.

7. Partition and Format New Capacity.

When the reconstruction is completed, enter the Disk Administrator. The

original drive is still shown as E: and is 12 GB.

You can now select the unpartitioned area, and create a primary partition of

4 GB. Format the new partition, and for this

example you will now have another drive (say F:) of 4 GB without rebooting.

You can exit the Disk Administrator and begin

use of the new capacity on the F volume.

If it is required that expanded capacity and the original capacity share the

same drive letter, this can be done but will

require rebooting NT. The added capacity must be partitioned as an extended

partition, then select the original and new

(extended) partition. Use the selection "Extend Partition" to make the two

partitions share the same drive letter (E: for

this example). You will need to reboot NT before any part of E: becomes

available again. If you accidentally enter more

capacity than is actually available, NT will detect the error upon rebooting

as it will execute a check-disk operation on

the extended volume.

Operating System and Data on the Disk Array

Sometimes it is desirable to have the OS and user data reside on the disk

array, either on the same logical drive (one

array) or on separate logical drives (two or more arrays). The advantage is

that the OS will reside on a redundant drive.

For the case where the disk array is used as the boot device and contains

user data, virtual sizing can still be used. The

key limitation is that NT only allows a FAT boot partition size of 4 GB or

less. The disk array can be configured with an

array just for the boot partition/OS and another array for user data. The

second array/logical drive would be used for

virtual sizing as detailed in the above steps. For this case, the boot

partition could not be used for capacity expansion.

If the OS and data need to be on a single array (and logical drive),

multiple partitions are needed for capacity expansion.

Enable Virtual Sizing for the logical drive. As in the above steps, the

logical drive will be shown with the virtual

capacity of 81,917 MB. Create a FAT boot partition of 4 GB or less for the

OS which will become the C: volume. Create a

second partition for the data which will become for example the D: volume.

The remaining virtual capacity can be used for

expansion by creating additional partitions as new volumes as explained

above.

Existing Installations Without Virtual Sizing Enabled

If you already are using the NetRAID controller without Virtual Sizing

enabled, but now wish to add capacity to an existing

volume, you will be limited in your options. Here are the likely scenarios

when Virtual Sizing has not been enabled.

Without Rebooting.

Unless Virtual Sizing is used, NT does not recognize new logical drives

unless rebooted. Any drive (logical or physical)

will not be seen under the Disk Administrator until rebooted.

With Reboot.

If a reboot is acceptable, then the server can be downed, Virtual Sizing

enabled in Express Tools, and the on-line

expansion process under NT can be followed. This will allow a single drive

to be added to an existing array.